1. Field of the Invention
The present invention relates to a developing device in which an electrostatic latent image formed on an image carrier is converted into a visible image in an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus
2. Description of the Related Art
`Impression development` is known as one of the developing methods which uses one-component developing agent. This method has the characteristic of causing the toner particles or the toner carrying member to come into contact with the electrostatic latent image at essentially zero relative peripheral speed, as shown in U.S. Pat. No. 3,152,012. Since no magnetic materials are required, this has many advantages such as making the apparatus capable of simplification and being made more compact while, at the same time, making coloring of the toner simple.
In the above impression development method, since developing is performed by pressing the toner carrying member on, or bringing it into contact with, the electrostatic latent image, the use of a developing roller which has elasticity and conductivity as the toner carrying member becomes necessary. In particular, when the electrostatic latent image bearing member is rigid, it is a vital condition that the developing roller should be composed of an elastic body to avoid damage to the latent image bearing member. Also, in order to obtain the already-known developing electrode effect or the bias effect, it is desirable to provide a conductive layer on the surface, or in the vicinity of the surface, of the developing roller, and to apply a bias voltage as required.
However, because, in this type of developing device which uses a developing roller, developing is performed by the pressure contact of the electrostatic latent image bearing member and a blade for the formation of a toner thin layer with the developing roller, the following problem occurs.
That is, a certain length of time is required for the full recovery of the conductive layer of the developing roller which is deformed by the pressure contact of the electrostatic latent image bearing member and the toner thin layer formation blade. Because of this, a state may occur in which developing is performed before full recovery from this deformation and this will result in image randomness at every single rotation of the developing roller.
In this way, in developing apparatus which used the impression development method hitherto, the surface of the developing roller was deformed due to the pressure contact with the electrostatic latent image bearing member and the developer thin layer formation means, and this deformed portion reached the developing area before it had fully recovered. As a result, there was a problem in that there was great deterioration of image quality due to the occurrence of density randomness and fogging.